Method of establishing communication between wells



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METHOD OF ESTABLISHING COMMUNICATION BETWEEN WLLLS Fi-led Dec.

2 Sheets-Sheet 1 INVENTOR. Haro/JE. Sa( /Q/ BY @W Sept. 6, i966 H. E. sTAADT 3,270,816

METHOD OF ESTABLISHING COMMUNICATION BETWEEN WELLS Filed DSC. 19. 1963 2 Sheets-Sheet 2 IMKENTOR. Haro/d5 67000/ QMMQWW 3,2%,816 @F ESTABLESHHNG CMMUNECATEN BETWEEN WELLS iarnid E Saad Tulsa, Ghia., assigner to The Dow (Chemicat loinpany, Midland, Mich., a corporation of iciaware Filed Ecc. i9, w63, Ser. No. BlfZtl l2 Claims. (Cl. loof-42) This invention relates to a method of obtaining subsurface communication between spaced apart earth wells, land particularly to a method of obtain-ing said communication thro-ugh a liquid soluble subsurface formation which extends between said wells.

Such communication is often desired in certain industries, such as subterranean gas storage, solution mining, production of petroleum, and certain water flooding operations.

AIt is known to fracture an earth formation from one well in an `attempt to establish communication with a neighborhing well. Sometimes the formation adjacent to 'both wells are fractured in making such attempts. Often, however, communication is not achieved because the frac tures so produced from each well do not themselves meet or, if only one well is fractured, the fracture does not extend to or intersect the unfractured well.

Communication between wel-ls oftentimes is desirable betiween a series of wel-ls; In petroleum fields fwhere yliquid ow for either production or injection such as by pumping is carried on, equipping a single well can serve an extensive area if the equipped well be` directly-communicated through the formation to other wel-ls.

Accordingly, a principal object of this invention is to provide an improved methcd of obtaining subterranean communication between earth wells.

Another object of this invention is to provide an improved method of obtaining communication between spaced apart earth wells through lan earth formation which is at least partially liquid soluble. v

A further object of this invention is to provide an improved method of production and injection of multiple wells penetrating an earth subsurface formation.

in accordance with this invention communication is established between two or more cased earth wells which are spaced apart by a predetermined distance, each of which penetrates a particular earth formation` by notohing the casing (if any) of a first well and the adjacent annulus of the earth formation in a vertically disposed plane which is at an acute angle with respect toa line drawn between the first weiland a second wel-l with which communication is to be obtained, and then'notching the casing (if anyof the second well and the annulus and adjacent earth formation thereof in a vertically disposed plane which is disposed at an acute `angle on the same side of a line between the wells as is the first notch and, if extended, would intersect the vertically disposed notch of the other well (or bore hole). Both wells are then fractured through the particular formation by pumping liquid under ypressure into each well and into the notched parts adjacent thereto t-o first break down the formation, and then additional liquid is pumped into each well to enlarge and extend the so-induced frac-tures towards each other.

Communication with a third and following wells may be established by the creation of a similar set of vertically connecting fractures using one of the first two treated wells as the point of origin for a second directionalized fracture and the third well as the origin of a fracture to connect therewith. By repeating this system a line of communicated 'wells can be created.

Further according to this invention communication wit-h a third and more wells be effected also by fracturing a ram iii fiatented Sept. d, Edd@ Because the fracture or fractures induced adjacent to each well are vertically disposed, and aredisposed at a predetermined acute angle with respect to a line drawn betiween the wells, intersection of the extended fractures of the wells4 is accomplished with greater certainty than has heretofore been obtainable. .v

The invention, as well as additional objects and Aadvantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing in which: y

FG. l is a diagrammatical view showing two spaced apart wells between which communication has been established in accordance with this invention;

FIG. 2 is a plan View of the fractured wells shown'in FIG. 1, and

FIG. 3 is a plan view of an alternative well arrangement in accordance with this invention.

` Referring to the drawing, there is shown a pair of bore holes 10, 12 which penetrate earth formation 14, 16 and a more or less liquid soluble formation 18 which may, for example, be a salt (NaCl) formation.

Each of the bore holes or wells 10, l2 terminates in the soluble formation 18 and has the usual casing 2Q, 2-2, respectively, disposed therein. The annulus between the casing and well bore wall in each well 10, l2 is lled with cement 24, 26, respectively, as is the space between the bottom of the casing and the bottom of each well bore.

The two well distance, about 20() ft. to 400 ft., for example.

` The casingZtl, 22 of each well is capped at its upper endl by a suitable casing head 2S, 36. A liquid reservoir 32 is` coupled through a valve 34, pump 36, line 3S and valve 40 to the casing head 28.` A similar liquid reservoir 42, valve 44, pump 46, line dS and valve 5t) are coupled to the casing head 3ft.

In addition, a valve 52, 54 is coupled to each of the casing heads 2S, 30, respectively.

The casing 2i) has a vertically extending slot 56 (about 2G ft. long, for example) disposed near the bottom of the casing string. A cut or slot extension 66 similar to the slot 56 extends through the adjacent cement of the annulus between the casing and well bore wall and into the adjacent formation t3 (salt, for example). Sec FIG. 2, also.

The casing 22 has a vertically disposed slot plus its extension 6ft through the cement 26 in the annulus and into the adjacent soluble formation 33. Each of the slots S6, 58 and their respective extensions dd, 60 are disposed at an acute angle with respect -to a line 62 drawn between -thecenters of the twovbore holes ld, 12, and both siots extend from the bore holes on the sante side of the line dit. An acute anglo of about 45 between the slot and the line 6G has proven very practical in assuring intersection of the extended fractures.

The slot in the casing plus its extension through the annulus and into the adjacent formation is ltnown as a notch, as used herein. It the well is tin-cased, the term notch refers to the slotted cut into the formation adje cent to the well bore.

The vertically disposed slots S, SS and their extensions 66, on, respectively, which penetrate through the cement and into the adjacent formation 18 are produced by any suitable means, such as are disclosed, for example in US. Patent No. 3,066,735, entitled Hydraulic etting Tool," and issued December 4, 1962, to Warren M. Zingg, where -a jet of liquid which contains abrasive materials is directed bores are spaced apart by the desired eerdere ,il i towards the casing and well bore wall. The slots 56, S3 and their extensions, for example, are made by moving the jet along a linear path as the jet is operated.

After the notching (slots plus extensions) of each well it?, iZ: is done, cach weil is given a formation tracturing treatment. For example, with the valves 3i', dil open, liquid (usually water) is pumped by means ot the pump 36 into the' casing 20 of the well itl and the pressure in the Well bore and in the vertically oriented notch 66 is increased until the formation t8 breaks down, and then liquid is pumped into theformation at a high rate to enlarge and extend the fracture or fractures 'lil produced lwhen the formation itil breaks down.

The well l2 is, though not necessarily simultaneously with thc well it), then given a similar formation fracturing treatment in which liquid from the reservoir 42 is pumped by means of the pump 46, line 4S and opened valves Lid, Sti into the casing 22. After the break down of Ithe `formationvl adjacent to the slot 58 and extension eil, liquid is pumped into the fracture to expand and extend it as is well known in the well treating art.

Fromftime to time during the fracturing treatment, it is desirable to shutdown the 4fracturing treatment ot one well to observe pressure variations at the well head which indicate that communication has been established between the Wells.

it is desirable that the rate of injection of liquid into the learth formations adjacent to each well be maintained at as high a rate as is practicable with the pumping equipment, which 'is available. injection rates 'of from 1 to 300 barrels per minute have been used, for example. High injection rates, in general, insure that amore rapid extension of the fracture will occur than it lower liquid injection rates are used.

While water has been mentioned as an example of airacturing liquid, saturated brine is often used, especiallyif the formation 32.8 is -a salt formation, as the fractu'ring liuid until such time as communication between the wells liti, l?. is established. After communication is established, fresh Water is-pumped into one well and removed from the other well untilenough salt (or other water soluble'lmaterial) is removed to insure sustained communication between the two wells.

Oils, such as petroleum fractions, and crude oils are also satisfactory fracturing liquids. Other satisfactory liquids are acid and other chemical solutions, particularly when the formation being treated is `at least partly soluble in such solutions. lf an oil or other liquid having no ability to dissolve the formation is used, it is usually preferable to use a propping agent such as sand or other particulate solids, as is well known in the iracturing art, along with the liquid. The propping agent serves to assure communication through the fracture when the hydraulic pressure upon the liquid is released. The use of a propping agent is optional when the liquid is a solvent for at least a part of the formation, as cornmunication is gained by dissolution of the formation.

Since the slot S6 and its extension no at the well itl and the slottl and its extension all at the well l2 are both vertically oriented and directed towards each other as heretofore described, the fractures 7l?, 72 produced at the wells i0, 'l2 will be more or less vertically oriented and, when extended, intersect, as along the line 74.

l With the two fractures being oriented at an angle with respect to one another and directed towards one another, intersection of the fracture (and consequently communication between the wells) is easily accomplished.

@ne method of communication with a third and further wells in accordance with this invention, as shown in FIG. 3, is exemplified by repeating the practice heretotore described in communicating the pair of boreholes itin, lila ot the drawing. Thus, further wells located approximately along the line described by extending the line 52a connecting' the pair of boreholes lila, ia may be connected by forming betweenv adjacent wells pairs of communicating fractures 76a, lila corresponding to fractures itland 72. The process of pumping i'luid into the `fractures to extend them to points of intersection 'may be carried out simultaneously on all the wells under consideration. it is also within the purview of this invention, where for example, insufilcient treating equipment is available, to pump iluid into the wells one at a time to extend fractures therefrom to achieve intersection with a fracture from an adjacent. well. For a well within a series ofinterconnected wells and having a fracture already present, the extension of a new fracture may be more readily achieved by temporarily plugging the existing fracture during the pumping operation. Temporary plugging may be carried out according to any suitable means, such as that disclosed, for example, in US. Patent No. 2,734,861, issued February 14, 1956 to Scott, ct al.

A third or following well to be fracture communicated in accordance with this invention may be located also along a line at roughly a right angle to that connecting the preceding pair of wells. Thus a further well 78 to be communicated with borehole l2 may be disposed on a Iline it@ describing roughly a right angle with connecting line 62 at borehole l2 and an acute angle with the fracture 72a. A fracture 82 from the further well is projected on the same side of the connecting line as is the fracture 72a of the adjacent borehole ft2 and at an acute angle tothe connecting line.

As an example of a pair of wells where communication may be established therebetween in accordance with this invention, the wells are separated from one another by about 400 feet. The wel-ls extend downwardly into a salt zone which is about feet thick, the top of the salt zone being at about 900 feet of depth.

it is desired to fracture lthe formation and establish communication at the bottom of the salt zone, and the wells are drilled to near the bottom of the salt zone, the casing strings run into the wells and the casing cemented in place.

Notching, eg., slitting of the casing and extending the slits through the annulus and into the adjacent formation, of one wel-l is vertically oriented and extended about 2G feet in length, from about 975 feet to 995 feet below the surface. The notch is disposed at an acute angle with respect to a tine drawn between the wells, as previously mentioned.

rhe other well casing is also notched vertically (through the casing, annulus and into the adjacent formation) at a depth below the surface o about 975 to 995 eet. The notch in the second welll is likewise disposed at an acute angle .with respect to a line drawn between the two wells.

The wells are then given a formati-on iracturing treatment as heretofore described to achieve the desired vertically oriented formation fractures which, when extendable, establish communication between the two wells.

lt the two wells cannotbe given formation tracturing treatments simultaneously because of the lack of' suliicient treating equipment, first fracture one well and then the other well is fractured While the break down pressures required to induce iractures vary considerably, salt formations (NaCl) gcnerally 4are rather easy to break down, the usual break down pressure being about t pound per foot of overburden depth. After break down oi the formation the pressure at which liquid is injected into the formation usually drops by a substantial amount as is well known iu the formation fracturing art. Y

While the invention has been principally described in connection with the establishing of communications between spaeed apart wells through a salt formation, method of the invention is'equally applicable to the cstablishment of communication tirough formations oi other types which are penetrated by spaced apart well bores. Further the invention may be practiced in uncased formations, such asin formations below the cased portion of a bore hole, or in sections ot a bore hole which otherwise are uncased. When the invention is practiced in an uncased section the formation is notched in a similar fashion as if casing were present and the remaining steps are followed as if casing were present.

While the notches heretofore mentioned have been continuous slots, notches comprising a line of separate bores extending through the casing (if any), annulus, and into the adjacent formation, the bores being close spaced from one another. Such bores may be made by perforating with bullets, shaped or other explosive charges, or by use of a device such as is disclosed in the previously referred to US. Patent No. 3,066,735, for example. The required spacing between adjacent perforations may vary from one r two inches to several inches, depending on the nature of the formation being fractured in accordance with this invention.

What is claimed is:

it A method of establishing subsurface communication between first and second earth Wells which are spaced apart by a predetermined distance, each of which penetrates a particular earth formation, comprising notching said formation of said first well along a predetermined depth range and in a vertically disposed plane which cxtends generally at an acute angle with respect to a line drawn between said first and second well and towards said second well with which communication is to be established, notching said formation of said second well in a vertically disposed plane at an acute angle with respect to said line drawn between said wells and which, if eX- tended, would intersect an extension of the vertically disposed notch of said first well, and hydraulically fracturing said particular earth formation from both wells through said notches until said fractures meet.

2. A method in accordance with claim 1, wherein said wells are fractured simultaneously.

3. A method in accordance with claim 1, wherein said particular earth formation is at least partially liquid soluble.

It.. A method yin vaccordance with claim 1, wherein said particular formation is water soluble.

5. lA method in accordance with claim it', wherein said partcular formation is principally composed of sodium chloride.

6. A- method in accordance with claim 1, wherein a brine solution is the treating argent used in hydraulically fracturing said particular formation.

'7. A imethod in accordance with claim 1, wherein the treating agent injection rate during said hydraulic frac- .turing is between l and 300 barrels per minute.

8. A method in accordance with claim 1, wherein said fractures intersect at an angle of approximately 90 degrecs.

9. A method in accordance with claim 1, wherein a particulate solid proppintg agent is used with said treating agent used in hydraulically fracturing said particular formation.

10. A method in accordance with claim 1, wherein said first and second wells are cased through said particular earth formation and notching said casing and adjacent annulus and thence said formation occurs in said first and second wells.

11. A method in accordance with claim 1, wherein each of said acute angles are approximately 45 degrees.

12. A method of establishing communication with subsurface earth formations Ihaving wells which are spaced apart by predetermined distances, each of which penetrates a particular earth formation, comprising not-ching said formation of a first well along a predetermined depth range and in a vertically disposed plane which extends generally at an acute angle with respect to a line drawn between said first well and a second well and towards said second well with which communication is to be established, notching said formation of said second well in a vertically disposed plane at an acute angle with respect to saidtline drawn between said wells and which, if extended, intersect an extension of the vertically disposed notch of said lirst well, hydraulically fracturing said particular earth formation from both wells through said notches until said fractures meet, repeating the foregoing steps with respect to at yleast a third well to place it in communication with said first and second wells and establishing liquid communication between the earth surface and said earth formation through less than all the wells in subsurface communication.

References Cited by the Examiner UNITED STATES PATENTS 2,758,653 s/1956 Desbrow 16s-421x 2,966,346 12/1960 Haart-.tai 166 42.1X 3,062,286 12/1962 wynie 16e-42.1 3,199,586 s/1965 Henderson 'et a1 166-9 CHARLES E. OCONNELL, Primary Examiner.

J. A. LEPPINK, Assistant Examiner. 

1. A METHOD OF ESTABLISHING SUBSURFACE COMMUNICATION BETWEEN FIRST AND SECOND EARTH WELLS WHICH ARE SPACED APART BY A PREDETERMINED DISTANCE, EACH OF WHICH PENETRATES A PARTICULAR EARTH FORMATION, COMPRISING NOTCHING SAID FORMATION OF SAID FIRST WELL ALONG A PREDETERMINED DEPTH RANGE AND IN A VERTICALLY DISPOSED PLANE WHICH EXTENDS GENERALLY AT AN ACUTE ANGLE WITH RESPECT TO A LINE DRAWN BETWEEN SAID FIRST AND SECOND WELL AND TOWARDS SAID SECOND WELL WITH WHICH COMMUNICATION IS TO BE ESTABLISHED, NOTCHING SAID FORMATION OF SAID SECOND WELL IN A VERTICALLY DISPOSED PLANE AT AN ACUTE ANGLE WITH RESPECT TO SAID LINE DRAWN BETWEEN SAID WELLS AND WHICH, IF EXTENDED, WOULD INTERSECT AN EXTENSION OF THE VERTICALLY DISPOSED NOTCH OF SAID FIRST WELL, AND HYDRAULICALLY FRACTURING SAID PARTICULAR EARTH FORMATION FROM BOTH WELLS THROUGH SAID NOTCHES UNTIL SAID FRACTURES MEET. 